Apparatus for lifting graphite electrodes

ABSTRACT

A lift plug for lifting a graphite electrode includes a main body and an insert coupled to one end of the main body, with the insert configured to mate with a graphite electrode to secure the lift plug to the graphite electrode. The lift plug also includes a lifting component coupled to the main body opposite the insert to lift the graphite electrode. The insert comprises a non-graphite material with a coefficient of thermal expansion (CTE) similar to graphite, such that the lift plug expands at a similar rate as the graphite electrode when heated so as to prevent locking at a joint between the lift plug and the graphite electrode.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is a non-provisional of and claims priority toU.S. Provisional Patent Application Ser. No. 62/796,454, filed Jan. 24,2019, the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate to lift plugs for use in liftinggraphite electrodes in a foundry, steel plant, or smelter, and withelectric furnaces of various types, including electric arc furnaces andinduction furnaces, for example.

Graphite electrodes are used in the metal industries to melt, refine,and smelt materials in electrothermal furnaces (e.g., electric arcfurnaces). The heat needed to melt metals is generated by passingcurrent (typically in excess of 50,000 amperes) through one or aplurality of electrodes, and forming an arc between the electrodes andthe metal. Graphite is used to form the electrode, as graphite is one ofthe only materials available that has both high levels of electricalconductivity and the capability of sustaining the extreme heat generatedin such a demanding environment. A typical graphite electrode used inarc furnaces is constructed as an electrode column consisting of aseries of individual electrodes joined together (by graphite pins) toform a single column. In this way, as electrodes are consumed during thethermal process, replacement electrodes can be joined to the column tomaintain a desired length of the column extending into the furnace.

In operation of an electric arc furnace, graphite electrodes need to belowered into and lifted out of a crucible in which metals/ingredientsare processed. Traditionally, electrodes are often lifted using alifting device or “lift plug” that screws into the socket of thegraphite electrode. In the past, these lift plugs have been made fromseveral known materials. As one example, lift plugs may have previouslybeen made (at least in part) from steel or aluminum. However, if a liftplug made of steel or aluminum is screwed into a hot graphite electrodesocket, the steel and aluminum will expand faster than graphite of theelectrode, which may cause the lift plug to lock itself into theelectrode joint. Thus, upon the lift plug getting hot and locking, itmay be very difficult to remove. The lift plug may eventually come freewhen the electrode and the plug cool to room temperature, but thecooling process may take considerable time. In a worst-case scenario,the lift plug will damage the graphite electrode socket consideringsteel can expand at nearly 10× the rate of graphite.

As another example, some lift plugs have previously been made in partfrom graphite. While graphite lift plugs can operate sufficiently insome furnace operations, the graphite material used to manufacture thelift plug is typically purchased from a graphite electrode company. Thatis, companies that sell graphite lift plugs have typically purchasedgraphite connecting pins from graphite electrode companies and fabricatethem into the inserts needed for the lift plug—with the lift plug thenbeing assembled, load tested, and sold to the metal manufacturers foruse with their furnace operation. However, the price of graphite hasrecently gone up 5-10× due to a worldwide shortage of high-qualityneedle coke in the graphite electrode industry, and this shortage ofgraphite has resulted in it being more difficult and cost prohibitive toacquire graphite for the manufacture of lift plugs.

Another drawback of graphite lift plugs is that the graphite is soft,and with repeated use and handling the graphite insert eventually wearsout (the threads get worn and damaged after repeated use) and the entirelift plug has to be replaced. Such replacing of graphite lift plugs canoccur on a frequent basis, which can be costly to an operator.

Therefore, it would be desirable to design an apparatus for liftinggraphite electrodes made from a cost-effective material(s) that providesproper performance and longevity.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, a lift plug configuredto lift a graphite electrode is provided. The lift plug includes a mainbody and an insert coupled to one end of the main body, the insertconfigured to mate with a graphite electrode to secure the lift plug tothe graphite electrode. The lift plug also includes a lifting componentcoupled to the main body opposite the insert to lift the graphiteelectrode. The insert comprises a non-graphite material with acoefficient of thermal expansion (CTE) similar to graphite.

In accordance with another aspect of the invention, a lift plug forlifting a graphite electrode includes a main body and a threadedconnection fixed at a first end of the main body and mateable withthreads of the graphite electrode, the threaded connection comprising anon-graphite material. The lift plug also includes a coupling attachedto a second end of the main body opposite the first end for lifting thegraphite electrode. The non-graphite material has a coefficient ofthermal expansion (CTE) of less than 3 (μm/(m K)) over a range from roomtemperature to 1000 degrees Fahrenheit.

In accordance with yet another aspect of the invention, a method ofmanufacturing a lift plug useable for lifting a graphite electrodeincludes providing a main body comprising a lifting bail and coupling aninsert to the main body on an end thereof opposite the lifting bail, theinsert configured to mate with a graphite electrode. The insertcomprises a non-graphite material with a coefficient of thermalexpansion (CTE) similar to graphite, within +/−0 to 1 (μm/(m K)) over arange from room temperature to 1000 degrees Fahrenheit.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate preferred embodiments presently contemplated forcarrying out the invention.

In the drawings:

FIG. 1 is a front plan view of an AC electric arc furnace system in orwith which embodiments of the invention may be implemented.

FIG. 2 is a cross-sectional front view of a portion of the AC electricarc furnace system of FIG. 1, according to an embodiment of theinvention.

FIG. 3 is a side top perspective view of a lift plug for liftinggraphite electrodes, according to an embodiment of the invention.

FIG. 4 is a side view of the lift plug for lifting graphite electrodesof FIG. 3, according to an embodiment of the invention.

FIG. 5 is a side view of the lift plug for lifting graphite electrodesof FIG. 4 shown 90 degrees from the side view of FIG. 4, according to anembodiment of the invention.

FIG. 6 is a perspective side view of graphite electrodes, each with alift plug coupled to a top end thereof, and positioned relative to an ACelectric arc furnace, according to an embodiment of the invention.

FIG. 7 is a side view of an overhead crane lifting a graphite electrodevia a lift plug, according to an embodiment of the invention.

FIG. 8 is an upper partial perspective view of a graphite electrode witha lift plug exploded therefrom, according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the invention relate generally to lifting devices or liftplugs and, more particularly, to a lift plug for lifting graphiteelectrodes in a foundry or steel plant. While embodiments of theinvention set forth in detail here below are directed to a liftingapparatus for use with graphite electrodes in an electric arc furnace(EAF), it is to be understood that embodiments of the invention areequally applicable for use with other types of electric furnaces. Forexample, the lifting apparatus may be used to lift a graphite columninto or out of an induction furnace or a submerged arc furnace, forexample. Furthermore, embodiments of the invention may be utilized notonly in melting operations, but also in smelting or refining operations,such as a ladle furnace where molten metal is refined both chemicallyand thermally.

Referring to FIGS. 1 and 2, an AC electric arc furnace system 10 isshown that is useable with embodiments of the invention. In theillustrated embodiment, the AC electric arc furnace system 10 includesan AC electric arc furnace 12 for heating and melting a desired material14 and a ladle 16 into which molten material may be poured.

The AC electric arc furnace 12 includes a refractory-lined meltingvessel 18 that holds a material to be melted and one or more electrodes20 (such as the three electrodes shown in FIGS. 1 and 2) used to heatand melt the material in the vessel 18. Each of the electrodes 20 isformed of a graphite material that has both high levels of electricalconductivity and the capability of sustaining extreme heat generated inoperation of the AC electrical arc furnace 12. The electrodes 20 may beround in section and formed in segments that may be joined together, sothat as the electrodes 20 wear, new segments can be added.

The refractory-lined melting vessel 18 includes a lower hearth 22 thatholds the material 14 to be melted, with a tap spout 24 included in thelower hearth 22 that allows molten material 14 to be poured out from thelower hearth 22. A roof 26 is positioned over the lower hearth 22 thatis removable therefrom. The roof 26 includes openings 28 formed thereinthrough which electrodes 20 may positioned and lowered down into thelower hearth 22.

In operation of electric arc furnace system 10, material 14 (e.g., scrapmetal, alloys, fluxes, ore) may be loaded into the lower hearth 22 ofrefractory-lined melting vessel 18. After loading of the material 14,the roof 26 is positioned over the lower hearth 22 and meltdown orrefining of the material 14 commences. The electrodes 20 are loweredinto the material 14 and an arc is struck between the charged material14 and the electrodes 20, with electrical phase currents in excess of50,000 amperes typically used to strike the arc. Lower voltages may beselected for this initial part of the operation to protect the roof 26and walls of lower hearth 22 from excessive heat and damage from thearcs. Once the electrodes 20 have reached a heavy melt at the base ofthe lower hearth 22 and the arcs are shielded by the material 14, thevoltage can be increased and the electrodes 20 raised slightly,lengthening the arcs and increasing power to the material 14. Duringmelting, the electric arc temperature reaches around 3000° C. (5000°F.), thus causing the lower sections of the electrodes 20 to glowincandescently when in operation. Once the material 14 has completelymelted down and a temperature and chemistry of the material is correct,the molten material 14 is tapped out into preheated 16 ladle throughtilting of the AC electric arc furnace 12 (i.e., tilting ofrefractory-lined melting vessel 18).

In operation of electric arc furnace system 10, it is necessary totransport the graphite electrodes 20 to/from the system, and toselectively raise and lower electrodes 20 from the melting vessel 18.For providing for such transporting and movement of the electrodes 20, alifting adaptor 100 is provided that is mateable with the electrodes 20and by which a translating mechanism, such as an overhead gantry orwinch (FIG. 7), may be connected to the electrode 20, to provide formovement thereof. The lifting adaptor 100 may be any suitable adaptor orconnector for lifting a graphite column, including a lift plug 104 asshown and described in FIGS. 3-8, and ideally is left connected to theelectrode 20 during operation of the electric arc furnace system 10 andheating of the electrode 20. According to embodiments of the invention,the lifting adaptor 100 (i.e., lift plug 104) includes one or morecomponents or parts that are composed of a material that has acoefficient of thermal expansion (CTE) similar to graphite, as will bedescribed in more detail hereafter. A lifting adaptor 100 made from amaterial with a CTE similar to graphite will expand at a similar rate asthe graphite column when heated, which will prevent locking at the jointbetween the lifting adaptor 100 and the graphite column.

Referring to FIGS. 3-5, a lifting adaptor 100 is shown as a lift plug104, in accordance with an embodiment of the invention. The lift plug104 is preferably configured to lift a graphite electrode. The lift plug104 may comprise a main body 106 and an insert 108 coupled to one end ofthe main body 106. The insert 108 is generally configured to mate with agraphite electrode to secure the lift plug 104 to the graphiteelectrode. The insert 108 may be manufactured from a “connecting pin”typically used to join two graphite electrode segments together, e.g.where graphite electrodes are continuously fed into the furnace. Theinsert 108 may be coupled between a first plate 110 and a second plate112 of the main body 106 by a plurality of fasteners 114. Alternatively,the insert 108 may be an integral component of the main body 106. Theinsert 108 may comprise a material with a CTE similar to graphite, aswill be explained in more detail with respect to FIG. 6. A liftingcomponent 116 is shown coupled to the main body 106 opposite the insert108 to lift a graphite electrode coupled to the lift plug 104. Thelifting component 116 may comprise a lifting handle (commonly referredto as a “lifting bail”) 118. According to an exemplary embodiment, theinsert 108 may have threads 120 that mate with corresponding threads onthe graphite electrode 20 (FIGS. 1 and 2) to secure the lift plug 104 tothe electrode.

Referring now to FIG. 6, a lift plug 104 coupled to a graphite electrode122 (i.e., a graphite column) of an AC electric arc furnace 124 (similarto the furnace 12 of FIGS. 1 and 2) is shown, according to an embodimentof the invention. The graphite electrode 122 may be used on an ACelectric arc furnace 124 in a shop or foundry or steel plant, with thefurnace having a graphite electrode holder 126, also referred to as agraphite column holder, positioned above the electric furnace.

The lift plug 104 includes a threaded end 120 that screws into a socket130 of the graphite electrode 122 having the mating threads. The liftplug 104 allows an overhead crane (or gantry crane) to pull the graphiteelectrodes 122 in and out of the AC electric arc furnace 124 (andtransport them therefrom) and handle the electrodes when they are inuse, with it thus recognized that the temperature of the lift plug 104will increase when coupled to a hot electrode.

According to an exemplary embodiment of the invention, the lift plug 104uses an insert 108 made of a non-graphite material having a coefficientof thermal expansion (CTE or a) that is similar to that of the graphiteelectrode 122. The non-graphite material has a CTE of less than 3 (μm/(mK)) over a range from room temperature to 1000 degrees Fahrenheit, ascompared to graphite having a CTE of around 1-2 at these temperatures.Thus, as the CTE of the non-graphite material from which insert 108 isformed is similar to the CTE of graphite, that is, within +/−1 (μm/(mK)) over a range from room temperature to 1000 degrees Fahrenheit, theinsert 108 will not expand faster, or significantly faster, than thegraphite electrode 122 when the lift plug 104 is screwed into thegraphite electrode 122. Thus, the chance of the lift plug 104 lockingitself into the joint/socket 130 of the graphite electrode 122 may beeliminated, such that the lift plug 104 can be easily removed from thegraphite electrode 122.

According to an exemplary embodiment of the invention, the non-graphitematerial from which insert 108 is formed is a nickel-iron alloy thatcontains approximately 30-36% Nickel, which may typically be referred toas Invar or a variant of Invar. Invar is a nickel-iron alloy knowngenerically as FeNi36, or 64FeNi (Invar 36) in the U.S., and there areseveral other variants of Invar having a composition of roughly 30-36%nickel that can use subtle additions of other alloys (e.g., cobalt) toimprove machinability or slightly modify the metallurgical properties.Examples of Invar variants include (but are not limited to) Super Invar32-5 (FeNi31Co5) and Inovco (FeNi33Co4.5), for example. It is thusunderstood that embodiments of the invention encompass lifting pluginserts 108 made from the above referenced Invar alloys, and it is alsoenvisions that other Invar alloys, alloys, and/or non-metallic materialsthat exhibit similar CTE, hardness, and/or strength characteristics asthese Invar alloys are considered to be within the scope of theinvention and suitable for use in lifting plug inserts 108 for use withgraphite electrodes 122. Accordingly, embodiments of the invention useInvar or a variant of it for the purpose of replacing graphite in a liftplug 104 for a graphite electrode 122. This very stable metallicmaterial may be substituted for the traditionally used graphite or steelin lift plugs 104 for lifting graphite electrodes 122.

Referring now to FIG. 7, an overhead crane 132 is shown lifting agraphite electrode 122 by a lifting adaptor 100 (e.g. lift plug 104),according to an embodiment of the invention. The overhead crane 132provides a system for mounting/positioning the graphite electrode 122 inan electric arc furnace 124 (FIG. 6), with the electric furnacecomprising a graphite electrode holder 126 (FIG. 6) to position thegraphite electrode 122 operably in the electric furnace. The systemfurther includes the lifting adaptor 100 comprising a lifting mechanism116 to lift the lifting adaptor 100, and a threaded end 120 coupled tothe lifting mechanism 116, with the threaded end 120 mating with athreaded socket formed in the graphite electrode 122. As previouslydescribed, the threaded end 120 may be composed/formed of a non-graphitematerial having desirable CTE and hardness characteristics, with thethreaded end 120 being formed of an Invar alloy or variant thereof,according to an exemplary embodiment. The overhead crane 132 receivesthe lifting mechanism 116 and can position the graphite electrode 122 inthe graphite electrode holder 126 (FIG. 6).

Referring now to FIG. 8, a graphite electrode 122 having threaded socket130 for receiving a threaded end 120 of a lift plug 104, is shownaccording to an embodiment of the invention. As referred to previously,the lift plug 104 comprises a main body 106 and a threaded connection120 fixed at a first end 134 of the main body 106. The threadedconnection 120 comprises threads of a non-graphite material to mate withthreads 136 of the graphite electrode 122, with the non-graphitematerial having a CTE similar to the graphite electrode 122. In someembodiments, the lift plug 104 comprises an insert 108 coupled to themain body 106 with the insert 108 comprising a threaded insert 138 toscrew into a threaded socket 130 of the graphite electrode 122. Asreferred to previously, the threaded connection 120 of the lift plug 104may be formed of an Invar alloy having a CTE similar to a CTE of thegraphite column up to 300-400 degrees Fahrenheit, or beyond (i.e., up to1000 Fahrenheit). The lift plug 104 and the socket 130 may have anysuitable number of threads per inch. According to some embodiments, thelift plug 104 and the socket 130 may have 2, 3, or 4 threads per inch. Acoupling 116 (e.g. lifting bail 118) is shown attached to a second end140 of the main body 106 opposite the first end 134 to lift the graphiteelectrode 122.

Beneficially, embodiments of the invention provide a lifting adaptorcoupleable to a graphite column for positioning the column in anelectric furnace. The lifting adaptor may comprise a main body having athreaded connection or insert fixed at a first end of the main body. Thethreaded connection is composed of a non-graphite material having a CTEsimilar to the graphite column, with an Invar alloy or variant of Invarbeing used for the threaded connection according to exemplaryembodiments. The lifting adaptor may also include a coupling attached toa second end of the main body opposite the first end to lift thegraphite column. The coupling may include a lifting bail attachable toan overhead crane to lift the graphite column into and/or out of theelectric furnace.

Therefore, according to one embodiment, a lift plug configured to lift agraphite electrode is provided. The lift plug includes a main body andan insert coupled to one end of the main body, the insert configured tomate with a graphite electrode to secure the lift plug to the graphiteelectrode. The lift plug also includes a lifting component coupled tothe main body opposite the insert to lift the graphite electrode. Theinsert comprises a non-graphite material with a coefficient of thermalexpansion (CTE) similar to graphite.

According to another embodiment, a lift plug for lifting a graphiteelectrode includes a main body and a threaded connection fixed at afirst end of the main body and mateable with threads of the graphiteelectrode, the threaded connection comprising a non-graphite material.The lift plug also includes a coupling attached to a second end of themain body opposite the first end for lifting the graphite electrode. Thenon-graphite material has a coefficient of thermal expansion (CTE) ofless than 3 (μm/(m K)) over a range from room temperature to 1000degrees Fahrenheit.

According to yet another embodiment, a method of manufacturing a liftplug useable for lifting a graphite electrode includes providing a mainbody comprising a lifting bail and coupling an insert to the main bodyon an end thereof opposite the lifting bail, the insert configured tomate with a graphite electrode. The insert comprises a non-graphitematerial with a coefficient of thermal expansion (CTE) similar tographite, within +/−0 to 1 (μm/(m K)) over a range from room temperatureto 1000 degrees Fahrenheit.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A lift plug configured to lift a graphiteelectrode, the lift plug comprising: a main body; an insert coupled toone end of the main body, the insert configured to mate with a graphiteelectrode to secure the lift plug to the graphite electrode; and alifting component coupled to the main body opposite the insert to liftthe graphite electrode; wherein the insert comprises a non-graphitematerial with a coefficient of thermal expansion (CTE) similar tographite.
 2. The lift plug of claim 1 wherein the non-graphite materialcomprises a nickel-iron alloy that contains approximately 30-36% Nickel.3. The lift plug of claim 2 wherein the nickel-iron alloy comprisesFeNi36.
 4. The lift plug of claim 2 wherein the nickel-iron alloycomprises FeNi31Co5 or FeNi33Co4.5.
 5. The lift plug of claim 1 whereinthe non-graphite material has a CTE of less than 3 (μm/(m K)) over arange from room temperature to 1000 degrees Fahrenheit.
 6. The lift plugof claim 1 wherein the non-graphite material has a CTE of approximately1-1.5 (μm/(m K)) at room temperature and a CTE of approximately 2 (μm/(mK)) between 300-400 degrees Fahrenheit.
 7. The lift plug of claim 1wherein the insert comprises a threaded insert to screw into a threadedsocket of the graphite electrode.
 8. The lift plug of claim 1 whereinthe lifting component comprises a lifting bail.
 9. A lift plug forlifting a graphite electrode comprising: a main body; a threadedconnection fixed at a first end of the main body and mateable withthreads of the graphite electrode, the threaded connection comprising anon-graphite material; and a coupling attached to a second end of themain body opposite the first end for lifting the graphite electrode;wherein the non-graphite material has a coefficient of thermal expansion(CTE) of less than 3 (μm/(m K)) over a range from room temperature to1000 degrees Fahrenheit.
 10. The lift plug for lifting a graphiteelectrode of claim 9 wherein the non-graphite material comprises anickel-iron alloy that contains approximately 30-36% Nickel.
 11. Thelift plug for lifting a graphite electrode of claim 10 wherein thenickel-iron alloy comprises FeNi36.
 12. The lift plug for lifting agraphite electrode of claim 10 wherein the nickel-iron alloy comprisesFeNi31Co5 or FeNi33Co4.5.
 13. The lift plug for lifting a graphiteelectrode of claim 9 wherein the main body comprises a first plate and asecond plate, and wherein the threaded connection is positioned betweenand secured to the first plate and the second plate.
 14. The lift plugfor lifting a graphite electrode of claim 9 wherein the non-graphitematerial has a CTE of approximately 1-1.5 (μm/(m K)) at room temperatureand a CTE of approximately 2 (μm/(m K)) between 300-400 degreesFahrenheit.
 15. A method of manufacturing a lift plug useable forlifting a graphite electrode, the method comprising: providing a mainbody comprising a lifting bail; and coupling an insert to the main bodyon an end thereof opposite the lifting bail, the insert configured tomate with a graphite electrode; wherein the insert comprises anon-graphite material with a coefficient of thermal expansion (CTE)similar to graphite, within +/−0 to 1 (μm/(m K)) over a range from roomtemperature to 1000 degrees Fahrenheit.
 16. The method of claim 15wherein the non-graphite material is a nickel-iron alloy that containsapproximately 30-36% Nickel.
 17. The method of claim 16 wherein thenickel-iron alloy comprises FeNi36.
 18. The method of claim 16 whereinthe nickel-iron alloy comprises FeNi31Co5 or FeNi33Co4.5.
 19. The methodof claim 15 further comprising forming a plurality of threads on theinsert to enable the insert to be screwed into a threaded socket of thegraphite electrode.
 20. The method of claim 15 wherein providing themain body comprises providing a main body having a first plate and asecond plate, and wherein coupling the insert to the main body comprisessecuring the insert between the first plate and the second plate, via aplurality of connection pins.